21. Find the center of mass of three point masses, shown above, arranged on the x axis: 6 kg at x =-2, 5 kg at x = 3 and 9 kg at x = 5. O 1.80 1.33 2.00 2.40 22. A sound wave in air travels at 340 m/s at an angle of 10 degrees when it strikes the surface of a lake. If the speed in water is 1482 my's, what is the angle that the sound wave travels through the water? 22.8 degrees 61.0 degrees 10.5 degrees 49.2 degrees 23. The period of a pendulum 2 meters long is 6.1 seconds on another planet. What is the acceleration due to gravity on this planet? 9.81 m/s2 2.12 m/s2 4.24 m/s2 4.49 m/8224. Find the average angular acceleration, in rad/sec, of a CD player that starts up from rest and comes up to operating speed at 150 rpm in 4 seconds. 0.625 rad/32 37.5 rad/$2 3.93 rad/s2 235 rad/s 25. A conductor that has zero resistance at very low temperatures is called a: Superconductor Insulator Semiconductor NonconductorV = 12 V R 1 + R 2 R3 26. In the circuit shown, if R , = 10 0, R2 = 20 0, and Ry = 30 0, what is the current through resistor 3? 30 A 12 A 0.40 A 0.04 A27. What angle is traversed, in radians, if a disk rotates from 30' with an angular acceleration of 10" in 12 seconds. 410 radians 944 radians 720 radians 556 radians 28. A 67.0 /C charge is placed 1.00 m from a 134 /C charge. Find the point between the two charges where the electric field is zero. 0.586 m from the 67.0 /C charge 0.414 m from the 67.0 AC charge 0.172 m from the 67.0 AC charge 0.828 m from the 67.0 /C charge 29. An ambulance is traveling at 30 m/'s away from you, while you are sitting on a park bench. If the siren emits a frequency of 880 Hz, what frequency will you hear? The speed of sound in air is 340 m/s. 809 Hz O 960 Hz 638 Hz 772Hz